Rogue weed marches through county

Unrecognized locally until two years ago, stinkwort is spreading despite defensive efforts

Volunteer Jeff Field yanks a stinkwort plant from the soil behind an elementary school near Tecolote Canyon Monday afternoon. He and Jim Roberts are trying to clear an invasive weed known as stinkwort, with the scientific name of Dittrichia graveolens, from the area around Tecolote Canyon before it takes off and spreads seeds.
— Peggy Peattie

Volunteer Jeff Field yanks a stinkwort plant from the soil behind an elementary school near Tecolote Canyon Monday afternoon. He and Jim Roberts are trying to clear an invasive weed known as stinkwort, with the scientific name of Dittrichia graveolens, from the area around Tecolote Canyon before it takes off and spreads seeds.
— Peggy Peattie

A group of native plant experts took a field trip in Poway two years ago and came across a species that none of them recognized.

Now, they all know stinkwort and have issued an all-points bulletin to “kill on sight.”

“It is carpeting school yards and swarming in many parks and open spaces in coastal San Diego County,” said Kay Stewart, local chapter president of the California Native Plant Society. “We need to get enough people on this to stop its spread.”

The annual plant, which scientists call Dittrichia graveolens, is a fall-flowering, sticky and aromatic annual the California Invasive Plant Council said appears to be rapidly expanding its range. The biggest infestation is in the Bay Area but San Diego County is the spot in Southern California county where stinkwort has its strongest foothold.

Stinkwort is part of the sunflower family and native to Africa, Asia and Europe. It resembles a small Christmas tree when small and grows to about three feet tall with yellow flowers.

The weed defies control and is known to return after wildfire. The only reliable method for getting rid of the flowering plants is removing by hand; spraying them with herbicide prompts the production dandelion-like seeds.

Nonnative plants are of widespread concern, particularly in temperate climates including San Diego’s where plants can grow year-round. Under the right conditions, invasive species spread rapidly and displace native plants, birds and animals by taking over landscapes.

Invasive weeds in San Diego County

Stinkwort is just one of several plants that threaten native habitats across the region. Others include:

Pampas grass : This saw grass grows so fast and makes so many seeds that it can create a major fire hazard in a few years if not removed when first found.

Saharan mustard : This vigorous weed is swarming over both deserts and coastal areas. It is very flammable when dry, and it fuels fires in the desert which destroy shrubs that may be decades or centuries old.

Garland daisy or chop suey green : These bright yellow or yellow-and white-annuals grow to 4 feet tall and fill up coastal canyons. They are edible when young but the wild ones are not very tasty.

Tocalote or Malta thistle : Very prickly and unpleasant to handle; tiny seeds scatter in large area downwind.

Periwinkle : Any shady canyon can become carpeted with this vine, which will bury all plants that might otherwise support wildlife in these critical habitats.

Puncturevine, punctureweed, caltrop or goathead : This little creeper with yellow flowers makes hundreds of 1/2-inch-wide seedpods with three thorns that will go through the sole of a shoe or a bicycle tire.

Ricegrass or smilograss : A vigorous grass taking over coastal San Diego County gardens, parks, and wild lands. Each big plant has tough stalks and flower stalks that poke up through shrubs to a height of 6 feet or more, with thousands of minuscule seeds.

Giant reed : Fills up canyons. Very flammable when dry and virtually useless for wildlife when not.

Source: California Native Plant Society, San Diego chapter

Stinkwort appears to love hard-packed soils such as those found in play fields, along with roadsides, and other “disturbed” lands. “If it’s specifically well-adapted to those kind of places … that means there can be some very big areas where it starts to aggressively expand from,” Stewart said.

There’s no official eradication plan for stinkwort in the county, just a network of concerned landscape architects, gardeners and plant lovers who are trying to raise the alarms now in hopes of minimizing its spread. The weed was first reported in California in 1984. It wasn’t found in San Diego County for nearly two more decades. Even then, it went largely unnoticed until the past year or two.

Jim Roberts of Clairemont has devoted recent weeks to removing stinkwort from Tecolote Canyon, Mission Bay and nearby areas. A retired physicist, Roberts first heard about the stinkwort last fall from a fellow native plant enthusiast and promised himself he’d make it a priority this year.

“My initial purpose was to keep it out of Tecolote,” he said. “To my dismay, I have discovered that stinkwort is growing on the grounds of several local schools.”

On Monday, he and a friend pulled stinkwort from a lot near his home. Before that, he convinced San Diego city parks crews to capture the rogue plant in Mission Bay and unsuccessfully sought help from the city to control stinkwort at Lake Miramar.

Given the plant’s ability to reproduce, Roberts isn’t particularly upbeat about his campaign. “There is a chance with a concerted effort it could be brought under control,” he said.

Success or failure will come into focus until about this time next year when Roberts can tell if seeds took root faster than he uprooted the plants.

Part of the difficulty is due to the stinkwort’s life cycle. It emerges over the summer and by late August the young plants are growing rapidly. By October, they blooming and in November, they make seeds, turn browns and withers into what Roberts calls a “bunch of ugly brown twigs.” By then, the seeds have been scattered by the wind.